Add a missing define for minizip, needed on some installations of zlib

diff --git a/simgear/package/ioapi.h b/simgear/package/ioapi.h
index 1dba776c7d6ec27b7213d5d3ff4e65c0fedca93b..cbc0e33e3f779b13d4271830b8c7a96daa8cf04e 100755 (executable)
--- a/simgear/package/ioapi.h
+++ b/simgear/package/ioapi.h
@@ -9,6 +9,11 @@
 #ifndef _ZLIBIOAPI_H
 #define _ZLIBIOAPI_H
 
+// Needed for some zlib installations:
+#ifndef OF
+  #define OF(x) x
+#endif
+
 
 #define ZLIB_FILEFUNC_SEEK_CUR (1)
 #define ZLIB_FILEFUNC_SEEK_END (2)